Intraocular lens and a polymer composition for making same

ABSTRACT

An intraocular lens comprises a UV-absorbing optic lens made of a polymer composition having the following light transmission spectrum in its visible postion at the following wavelengths: 400 nm, 10 to 27 percent of light transmission; 420 nm, 21 to 37 percent; 440 nm, 37 to 55 percent; 460 nm, 52 to 63 percent; 480 nm, 70 to 78 percent; 560 nm, 85 to 90 percent; 520 to 650 nm, 90 to 95 percent, and incorporating ingredients taken in the following mass percent ratio: 
     
         ______________________________________                                    
 
    
     UV-absorbing material  1.65 to 3.0                                        
(4-alkoxy-2-hydroxybenzophenone                                           
or tetraoxybenzophenone)                                                  
fat-soluble dye-4-(2,4-dimethylphenylazo)-                                
                       0.011 to 0.016                                     
5-methyl-2-phenyl-1,2,3-triazole                                          
dibutylphthalate        4.8 to 5.0                                        
polymethylmethacrylate to make up 100%.                                   
______________________________________

FIELD OF THE INVENTION

The present invention relates generally to ophthalmology and morespecifically to an intraocular lens for correction of sight after anoperative ablation of the natural crystalline lens, as well as to apolymer composition for making said intraocular lens.

BACKGROUND OF THE INVENTION

Known in the present state of the art are intraocular lenses whose opticlenses are made of polymethylmethacrylate and provide for optical eyecorrection after removal of the natural crystalline lens.

However, such intraocular lenses fail to protect the retina from beingdamaged by UV or short-wavelength visible light.

The closest to the herein-proposed intraocular lens are UV-400 lenses,comprising a UV-absorbing optic lens made of apolymethylmethacrylate-based polymer composition and a UV-absorbingsubstance, such as 2,4-dihydroxybenzophenone.

Such optic lenses protect the retina against damage by light atwavelengths shorter than 380 nm, while such intraocular lenses closelyresemble, in the visible light spectrum, natural crystalline lenses ofyoung people aged under the age of 25 and feature the followingtransmission factor values on a wavelength of: 400 nm, 1.5 percent, 420nm, 55 percent; 440 nm, 82 percent, while on wavelengths in the range of460 to 650 nm said factor is within 93 and 95 percent.

However, with the aforesaid light transmission percentage values of theknown intraocular lenses an excess amount of light gets into the eyewithin a range of 400 to 480 nm, which precludes obtaining to thegreatest extent of restoration of visual acuity and color perception nordoes it enable one to bring to a normal level the protection of theretina against damage with light waves shorter than 480 nm in patientsover the age of 25. Besides, the polymer composition used for makingsuch intraocular lenses fails to produce such lenses that wouldcorrespond, as for their spectral characteristics, to the naturalcrystalline lenses of people older than 25.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an intraocular lensand a polymer composition for making the same, which would make itpossible to obtain an optic lens that would correspond, as for itsspectral characteristics, to the natural crystalline lenses of peopleover the age of 25 and that, when implanted, would increase the degreeof restoration of visual acuity and color perception.

In keeping with the foregoing and further objects, in an intraocularlens, comprising a UV-absorbing optic lens, according to the invention,said optic lens is made of a material featuring the following lighttransmission spectrum in its visible portion at the followingwavelengths: 400 nm, 10 to 27 percent of light transmission; 420 nm, 21to 37 percent; 440 nm, 37 to 55 percent, 460 nm, 52 to 63 percent; 480nm, 70 to 78 percent; 500 nm, 85 to 90 percent; 520 to 650 nm, 90 to 95percent.

Said object is accomplished also due to the fact that in a polymercomposition for making said intraocular lens, incorporatingpolymethylmethacrylate and a UV-absorbing material, according to theinvention, said polymer composition comprises, as said UV-absorbingmaterial, 4-alkoxy-2-hydroxybenzophenone or tetraoxybenzophenone, andincorporates additionally a fat-soluble dye, such as,4-(2,4-dimethylphenylazo)-5-methyl-2-phenyl-1,2,3-triazole, as well asdibutylphthalate as a plasticizer, with the following ratio of theaforesaid ingredients (in mass percent):

Practical application of the proposed intraocular lens having theaforesaid light transmission spectrum of its optical lens provides fortransmission of blue light equivalent to its transmission by the naturalcrystalline lenses of people older than 25, which ensures more completerestoration of visual acuity and color perception, as well as rendersthe coursing of the postoperative period milder and cuts down itsduration. In addition, the proposed intraocular lenses protect theretina against premature ageing and adds to visual comfort.

Use of the proposed polymer composition for making intraocular lenses,due to an appropriately selected qualitative and quantitative ratio ofits ingredients, provides for obtaining the abovementioned spectralcharacteristics of the proposed intraocular lens, which are based on thecombination of the spectral properties of the proposed dye andUV-absorbing material, the aforesaid spectral characteristics within arange of 430 to 650 nm being ensured due to the spectral properties ofsaid dye, and those within a range of 380 to 430 nm, due to combinationof the spectral properties of the dye and of the UV-absorbing material.

Any increase or decrease in the limits of the ingredients making part ofthe aforesaid composition results in optic lens spectral characteristicswhich go beyond the proposed limits, which affects adversely visualacuity and color perception in patients and leads to injuries to theretina by the light having a wavelength shorter than 380 nm.

The aforesaid percentage ratios between the ingredients incorporatedinto the proposed polymer composition are decisive in judging whetherthe formulations of the composition agree with the spectralcharacteristics of the proposed intraocular lens, so that the limitingvalues of the composition formulation depend on the thickness of theoptic lens of said intraocular lens, that is, the lower limiting valuesof the composition ingredients refer to thick (500 to 630μm) intraocularlenses, the upper limiting values refer to `thin` (300 to 380m)intraocular lenses, and the intermediate values refer to `medium` (400to 480μm) intraocular lenses, as indicated in Table 1 hereinbelow.

In the proposed composition the UV-absorbing material (i.e.,4-alkoxy-2-hydroxybenzophenone or tetraoxybenzophenone) takes part information of the intraocular lens spectral characteristics (that is,restricts penetration of short-wavelength light onto the retina), aswell as serves a light-stabilizer of the dye against possible fading.Apart from its conventional application as a plasticizer,dibutylphthalate is used also as an additional UV-absorbing material.

The fat-soluble dye, i.e.,4-(2,4-dimethulphenylazo)-5-methyl-2-phenyl-1,2,3-triazole has thefollowing structural formula: ##STR1## Said dye is hydrophobic, stainsthe polymer composition uniformly and provides for optical purity of thelens with a preset light transmission spectrum, since the dye neitherreflects nor diffuses light and moreover it is not washed out of theoptic lens.

Thus, intraocular lenses made from the proposed polymer material, arenontoxic and optically pure, they correspond, as for their spectralcharacteristics, to natural crystalline lenses of people over the age of25, and provide for more complete rehabilitation of the visual functionsof patients after implantation of such lenses.

Detailed Description of the Invention

For a better understanding of the present invention, given below are thefollowing examples of specific practical embodiment thereof given by wayof illustration.

The intraocular lens comprises a UV-absorbing optic lens made of amaterial featuring the following light transmission spectrum in itsvisible portion at the following wavelengths: 400 nm, 10 to 27 percent;420nm, 21 to 37 percent; 440nm, 37 to 55 percent; 460nm, 52 to 63percent; 480nm, 70 to 80 percent; 500nm, 85 to 90 percent; 520 to 650nm,90 to 95 percent, a 50-percent transmission point lying within awavelength range of 430 and 455nm.

To produce an intraocular lens with such a light transmission spectrumof its optic lens, use is made of a polymer composition, incorporatingpolymethylmethacrylate, a UV-absorbing material, a fat-soluble dye,i.e., 4-(2,4-dimethylphenylazo-5-methyl-2-phenyl-1,2,3-triazole, anddibutylphthalate as a plasticizer, with the following ratio of theaforesaid ingredients (in mass percent):

    ______________________________________                                        UV-absorbing material                                                                              1.65 to 3.0                                              fat-soluble dye      0.011 to 0.016                                           dibutylphthalate     4.8 to 5.0                                               polymethylmethactylate                                                                             to make up 100%,                                         ______________________________________                                    

wherein the aforesaid UV-absorbing material is4-alkoxy-2-hydroxybenzophenone or tetraoxybenzophenone.

Exemplary compositions for making the proposed intraocular lenses areproduced by the method of enblock radiation-induced polymerization inthe presence of isobutyric acid azodinitrile as a polymerizationinitiator.

EXAMPLE 1

There are taken weighed portions of the reaction mixture initialconstituents in the following amounts: methylmethacrylate, 93.274 g;fat-soluble dye, i.e.4-(2,4-dimethylphenylazo)-5-methyl-2-phenyl-1,2,3-triazole, 0.016 g;UV-absorbing material, i.e., 4-alkoxy-2-hydroxybenzophenone, 1.65 g;dibutylphatalate-plasticizer, 5 g; polymerization initiator (isobutyricacid azodinitrile), 0.06 g. The aforelisted ingredients are placed in aglass flask at room temperature and are made to completely dissolve inmethylmethacylate under constant stirring by a mechanical agitator. Thenthe mixture is passed through a capron filter, vacuumized at a residualpressure of 120 to 140 mm Hg and cast in moulds composed of two polishedsilicate glass pieces provided with a spacer in the form of a PVC tubearranged along the mould perimeter. Moulds filled with the mixture areplaced in an air-fed polymerization cabinet. The polymerization processproceeds for 10 to 12 hours.

Upon completion of polymerization the moulds are discharged from thepolymerization cabinet and the finished specimen is separated from thesilicate glass, thus obtaining the polymer composition incorporating thefollowing ingredients (in mass percent):

    ______________________________________                                        polymethylmethacrylate  93.334                                                UV-absorbing material-4-alkoxy-2-hydro-                                                               1.65                                                  xybenzophenone                                                                fat-soluble dye-4-(2,4-dimethylpheny-                                                                 0.016                                                 lazo)-5-methyl-2-phenyl-1,2,3-triazole                                        dibutylphthalate        5.0.                                                  ______________________________________                                    

EXAMPLE 2

There are taken weighed portions of the reaction mixture initialconstituents in the following amounts: methylmethacrylate, 92.926 g;fat-soluble dye, i.e.,4-(2,4-dimethylphenylazo)-5-methyl-2-phenyl-1,2,3-triazole, 0.014 g;UV-absorbing material, i.e., tetraoxylbenzophenone, 2.10 g;dibutylphathalate as a plasticizer, 4.9 g; polymerization initiator,i.e., isobutyric acid azodinitrile, 0.06 g. The ingredients areintermixed and polymerization is carried out according to the proceduredescribed in Example 1. The result is the polymer composition composedof the following ingredients (in mass percent);

    ______________________________________                                        polymethylmethacrylate   92.986                                               UV-absorbing material-4-alkoxy-2-hydroxy-                                                              2.10                                                 benzophenone                                                                  fat-soluble dye-4-(2,4-dimethylpheylazo)-                                                              0.014                                                5-methyl-2-phenyl-1,2,3-triazole                                              dibutylphthalate         4.90                                                 ______________________________________                                    

EXAMPLE 3

There are taken weighed portions of the reaction mixture initialconstituents in the following amounts: methylmethacrylate, 92,528 g;fat-soluble dye, i.e.,4-(2,4-dimethylphenylazo)-5-methyl-2-phenyl-1,2,3-triazole, 0.012 g;UV-absorbing material, i.e., 4-alkoxy-2-hydroxybenzophenone, 2.60 g;dibutylphthalate as a plasticizer, 4.8 g; polymerization initiator, i.e.isobutyric acid azodinitrile, 0.06 g. The ingredients are intermixed andpolymerization is carried out according to the procedure described inExample 1. The result is the polymer made up of the followingingredients (in mass percent):

    ______________________________________                                        polymethylmethacrylate  92.588                                                UV-absorbing material-4-alkoxy-2-                                                                     2.60                                                  hydroxybenzophenone                                                           fat-soluble dye-4-(2,4-dimethylphenylazo)-                                                            0.012                                                 5-methyl-2-phenyl-1,2,3-triazole                                              dibutylphthalate        4.80                                                  ______________________________________                                    

EXAMPLE 4

There are taken weighed portions of the reaction mixture initialcomponents in the following amounts: methylmethacrylate, 92.129 g;fat-soluble dye, i.e.,4-(2,4-dimethylphenylazo)-5-methyl-2-phenyl-1,2,3-triazole, 0.011 g;UV-absorbing material, i.e., tetraoxybenzophenone, 3.00 g;dibutylphthalate, 4.8 g; polymerization initiator, i.e. isobutyric acidazodinitrile, 0.06 g. The ingredients are intermixed and polymerizationis carried out according to the procedure described in Example 1. Theresult is the polymer composition made up of the following ingredients(in mass percent):

    ______________________________________                                        polymethacrylate        92.189                                                UV-absorbing material-tetraoxybenzophe-                                                               3.00                                                  none                                                                          fat-soluble dye-4-(2,4-dimethylphenylazo)-                                                            0.011                                                 5-methyl-2-phenyl-1,2,3-triazole                                              dibutylphthalate        4.80                                                  ______________________________________                                    

Intraocular lenses made of the polymer composition prepared as describedin Examples 1 to 4, feature the aforementioned light transmissionspectra whose parameters are ensured due to an appropriate ration of theingredients making part of said composition, as well as depend on thethickness of a given intraocular lens (i.e., on its dioptic power and onthe thickness of a specific model of the intraocular lens). Forinstance, Table 1 contains data on light transmission by the optic lensof the intraocular lens versus said dye content of the polymercomposition.

                  TABLE 1                                                         ______________________________________                                                Light transmission percent at a given ratio                                   between dioptric power (D), thickness of                                      intraocular lens across the central axis,                                     μm and dye concentration, %                                                  7-10 D,  11-12 D, 13-15 D,                                                    300 to   400 to   440 to                                            Light wave-                                                                             380 μm                                                                              420 μm,                                                                             480 μm,                                                                           16-25 D, 500 to                            length, nm                                                                              0.016%   0.014%   0.012% 630 μm, 0.011%                          ______________________________________                                        under 360 not over 0.014%                                                     380       not over 0.5                                                        400       25 to 27 24 to 26 24 to 27                                                                             10 to 23                                   420       28 to 37 29 to 31 28 to 32                                                                             21 to 32                                   440       38 to 55 38 to 40 38 to 42                                                                             37 to 50                                   460       54 to 63 54 to 56 54 to 58                                                                             52 to 57                                   480       73 to 78 74 to 75 75 to 76                                                                             70 to 76                                   500       87 to 90 87 to 88 87 to 88                                                                             85 to 88                                   520       92 to 94 92 to 93 92 to 93                                                                             90 to 93                                   540 to 650                                                                              94 to 95 94 to 95 94 to 95                                                                             94 to 95                                   ______________________________________                                    

With the limiting values of the amount of the dye specified for a givendioptric power, the spectral characteristic of the optic lens will gobeyond the limits proposed herein, which will affect adversely thepatient's visual acuity and color perception.

According to the trials performed, practical application of the materialfor the optic lens of the intraocular lens featuring the abovementionedspectral characteristics adds to the degree of visual acuity restorationby 10 to 25 percent compared with the prototype. Table 2 presents thefindings of experiments carried out on 12 advanced-age patients withpseudoaphakia. The patients' visual acuity was estimated by the ratiobetween the distances at which a tabular Landolt's ring can bedistinguished when looked at through a light filter featuring theherein-proposed spectral characteristics and through another lightfilter having the spectral characteristic of the prototype, theestimation being carried out according to one of the commonly adoptedtechniques. All measurements were performed in daylight.

                  TABLE 2                                                         ______________________________________                                                 Visual acuity with spectral characteristics:                                  proposed intraocular lens                                                     according to limiting values:                                              Patient's                                                                              short wave-                                                    Nos   age      length     long wavelength                                                                          prototype                                ______________________________________                                        1     49       1.14       1.18       1.02                                     2     63       1.10       1.27       1.06                                     3     50       1.20       1.31       1.04                                     4     57       1.20       1.37       1.05                                     5     70       1.21       1.40       1.05                                     6     62       1.21       1.45       1.07                                     7     50       1.11       1.24       1.02                                     8     51       1.18       1.35       1.04                                     9     60       1.19       1.39       1.04                                     10    80       1.10       1.25       1.03                                     11    65       1.10       1.21       1.04                                     12    59       1.04       1.11       1.02                                     ______________________________________                                    

According to the evidence contained in Table 2, a percentage increase invisual acuity is 25.4±2.7 on the average, compared with the prototypefor the long-wavelength limiting value of the spectral characteristicsof the proposed intraocular lens, and 11±1.5 for the short-wavelengthlimiting value.

The adopted ratios between the ingredients of light-filtering additivesmaking part of the polymer composition, and the dioptric power of theproposed optic lens of the intraocular lens enable one to produceintraocular lens with due account of prognosticated age-dependentchanges in the spectral characteristics of natural crystalline lenses.

Thus, the chief features of the invention are the light transmissionfactors within the wavelength range of 420 to 520 nm, ensured due to thequalitative and quantitative characteristics of the proposed polymercomposition. Table 3 contains comparative data on light transmissionfactors of the proposed intraocular lens and of the prototypeintraocular lens.

                  TABLE 3                                                         ______________________________________                                        Light wavelength,                                                                         Light transmission, %                                             nm          Proposed intraocular lens                                                                      Prototype                                        ______________________________________                                        420         21 to 37         55                                               440         37 to 55         82                                               460         52 to 63         93                                               480         70 to 78         95                                               500         85 to 90         95                                               520         90 to 94         95                                               ______________________________________                                    

An analysis into the light transmission spectra of natural crystallinelenses, of the proposed intraocular lenses, and of the prototype hasdemonstrated that the proposed intraocular lenses correspond, as fortheir spectral characteristics, to the natural crystalline lenses inpeople aged 50 and over. It is due to the abovesaid fact that the opticlens of the proposed intraocular lens provides for a normal degree ofoptical protection afforded to the retina against damage by light in thewavelength range of 420 to 480 nm in advanced-age people whose retina isto a greater extent vulnerable by luminous radiation. Thereby the amountof light absorbed by the retinal blue-sensitive cones within a range of420 to 480 nm is reduced by 40 percent compared with the prototype. Thisgives evidence that the proposed intraocular lens provides for morecomplete restoration of patient's color perception and fuller protectionof the retina against detrimental effect of light. The proposedintraocular lenses are readily implanted in patients of any age, makingallowance for future age dependent changes of the patient's naturalcrystalline lenses.

INDUSTRIAL APPLICABILITY

The polymer composition can be used for making intraocular lense of anymodels based on polymethylmethacrylate which provide for optical eyecorrection after removal of the natural crystalline lens.

We claim:
 1. An intraocular lens comprising a UV-absorbing optic lenscomprising polymethylmethacrylate, 4-alkoxy-2-hydroxybenzophenone ortetraoxybenzophenone as a UV-absorbing material,4-(2,4-dimethylphenylazo)-5-methyl-2-phenyl-1,2,3-triazole, anddibutylphthalate as a plasticizer, said components being present in thefollowing weight percent ratio:

    ______________________________________                                        UV-absorbing material                                                                             1.65 to 3.0                                               4-(2,4-dimethylphenylazo)-5-                                                                      0.011 to 0.016                                            methyl-2-phenyl-1,2,3-triazole                                                dibutylphthalate     4.8 to 5.0                                               polymethylmethacrylate                                                                            balance                                                   ______________________________________                                    

wherein the lens is made of a material having the following lighttransmission spectrum in its visible portion at the following wavelengths: 400nm--10 to 27 percent of light transmission; 420 nm--21 to 37percent; 440 nm--37 to 55 percent; 460 nm--52 to 63 percent; 480 nm--70to 78 percent; 500 nm--85 to 90 percent; and 520-650 nm--90 to 95percent.